of the undesirable adsorption of lithium (Li+), the analyte of interest, which competes for the active sites of the resin (SUBASINGHE; REZAEE, 2025). The stabilization of the system into a steady state reflects the limit of the resin's loading capacity under specific conditions. In an ideal purification scenario, the resin must exhibit significantly higher selectivity for impurities (Mg > Ca > Na > Li), ensuring that lithium retention remains reversible. Therefore, the evaluation of LiOH mass loss to the solid phase is a critical parameter for determining the economic viability and separation efficiency of the purification process at an industrial scale (BU, Y. et al. 2025). According to Ahmed (2024), obtaining high-purity precursors is imperative for the synthesis of advanced cathodic materials, such as lithium iron phosphate (LiFePO4), lithium manganate (Li2MnO4), and lithium cobalt oxide (LiCoO2). The production chain frequently utilizes lithium carbonate (Li2CO3) or lithium chloride (LiCl) as initial feedstocks for the crystallization of lithium hydroxide monohydrate (LiOH·H2O). The present study aims to investigate the dynamic performance of IRC 747 and IRC 748 resins to identify operational conditions that favor maximum selectivity for divalent contaminants over minimum retention of monovalent cations. Preliminary results indicate that the IRC 747 resin exhibits high efficacy, removing up to 76% of Ca2+ and 92% of Mg2+, thus consolidating its position as a robust alternative for the production of high-purity lithium solutions. Considering the requirement to refine lithium hydroxide (LiOH) solutions to battery-grade standards, this work aims to investigate the operational conditions that promote maximum selectivity of AmberSep™ IRC 747 and IRC 748 resins toward divalent calcium (Ca2+) and magnesium (Mg2+) ions. The research is based on the analysis of the dynamic behavior of the fixed-bed system, aiming to identify the equilibrium point at which the polymeric matrix exhibits minimum affinity for monovalent cations, such as lithium (Li+) and sodium (Na+). This differentiation in affinity is crucial to mitigate the undesirable retention of the analyte of interest, ensuring that the final polishing process results in a high-purity solution with the lowest possible mass loss. Specifically, the study evaluates the influence of flow rate variations (10 to 30 mL·min⁻¹) and ion exchange capacity on the mass transfer zone. Therefore, it seeks to establish a methodological protocol that utilizes selective chemisorption to remove contaminants that compromise the lifespan and safety of lithium-ion battery cathodes, such as LiFePO4 and LiCoO2. The ultimate goal is to validate the effectiveness of these chelating resins in consecutive sorption-desorption cycles, ensuring the technical and economic viability of producing purified precursors (TADESSE et al., 2019). The attainment of lithium hydroxide (LiOH) solutions meeting battery-grade specifications necessitates the elimination of metallic cations such as Mg2+, Ca2+, and Na+, a task for which ion exchange technology demonstrates technical superiority over conventional chemical precipitation. While precipitation processes are constrained by the thermodynamic equilibrium of the solubility product (Ksp), which precludes reaching ultra-high purity levels, chelating resins enable the polishing of solutions to concentrations in the parts per billion (ppb) range 103
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